It is known that a structuring of the illumination can be employed in order to achieve confocal depth discrimination in wide angle or with partial illumination of the image field (e.g., linear illumination). By means of a phase shift of the structured illumination, a depth-discriminated optical section can then be calculated, thereby producing the desired image of the object. As described, for example, in M. A. A. Neil et al., “Method of obtaining optical sectioning by using structured light in a conventional microscope” Optics Letter 22(24) 1997, 1905-1907, this can be achieved with three phase images at 0°, 120° and 240°.
In order to structure the illumination, either grids in the illumination beam path, interference of coherent partial rays or the employment of diffractive optical elements are proposed. A disadvantage is the inflexibility caused, since, when changing the objective lens of a laser microscope, a change in the structuring is also generally required. As a rule, a different grid must be provided for this, the interference of coherent partial beams must be changed or a different diffractive optical element must be employed.
In order to achieve increased resolution, a structuring close to the limiting frequency of the illumination side of the objective lens is necessary. Frequently, this is achieved only with a low modulation depth and/or a low illumination-side efficiency.
In addition, the generally low illumination intensity (in particular the low efficiency on the illumination side for the aforementioned resolution increase) is disadvantageous, if nonlinear specimen change effects are to be achieved.